A Compost Refresher

So by now you know composting involves layering roughly equal parts carbon- and nitrogen-rich waste, but you might be unclear on exactly which of the two are found in a particular kind of waste. The quick guide below, based on some handy charts from the University of Illinois Extension, indicates which nutrient is provided by compostable materials, which to avoid, and how to handle the tricky bits.

The Tricky Bits

Cardboard (C) – Slow to decompose; shred and soak before adding to compost pileCorn Cobs (C) – Slow to decompose; chop into small pieces and mix with nitrogen-rich materialDiseased Plants (C) – Bake in sun until thoroughly dried, burn, or add to a hot compost pile reaching 131-140 degrees FChemically-Treated Lawn Clippings (C+N) – wait 2-3 weeks before using treated clippings or allow to compost for 12 monthsNut Shells (C) – Very slow to decompose; pulverize or use as roughagePeat Moss (low in nutrients) – Slow to decompose and very absorbent; use in small quantity and mix wellPine Debris (C) – Very acidic and slow to decompose; use sparingly in compost for vegetable applicationRhubarb (N) – Contains oxalic acid which deters beneficial microbes; use sparingly and mix wellSawdust (C) – Can restrict aeration, add in thin layers and turn pile regularlySod N – Slow to decompose; compost roots-up on top of pile or separately under cardboard or a dark tarpWalnut Leaves (C) – Can be toxic to plants; add in small quantities and avoid contact with other plants for 30-40 daysWeeds (C+N) – Roots and seeds can be hard to kill; bake in sun before adding to a hot pile for at least another weekWood Ash (alkaline) – Can change pile chemistry and cause nutrient imbalance; do not add to top of pile and use in thin layers

To Avoid

Bones – Can attract pests and disease; consider making bone meal insteadCat Litter – Clay, perfumes, and chemicals are not plant-friendly; switch to a natural litter, like wood chips, that you can compostDairy Products – Very slow to decompose and attract pestsGlossy Paper – May contain toxic inksHuman Feces – Requires very high temperatures to kill pathogens and parasites; should be composted carefully over a number of years before handling. See The Humanure Handbook if you want to learn more.

Intrepid Gardens began in February 2013 as an experimental garden in Colombo, Sri Lanka seeking to provide families and community partners with the resources to grow sustainable food systems in tropical and urban landscapes. With our own 60 square foot rooftop slab, we began experimenting with growing solutions any urbanite could use. Here we share applications and news in permaculture, organics, and sustainable urban living.